The invention relates to a recycling steam system and in particular to means for improving the quality of return condensate supplied to the steam generator of the system.
A typical steam system of the character indicated includes a turbine exhausting to a surface condenser, wherein condensate accumulates in the hot well of the condenser, prior to return as recycled feedwater to the steam generator, there being heater and pump means in the return line to serve the feedwater requirements of the steam generator. Make-up water, seal leakage at sub-atmospheric pressure zones of the power cycle are among sources of uncondensable gases, such as oxygen, dissolved in the condensate, and other non-condensable gases are released by water-treatment chemicals. Such non-condensable gases, particularly the oxygen, are corrosive on mechanical parts of the system.
The problem is particularly pronounced at system start-up, when water in the condenser is saturated with oxygen (air), and it is conventional to adopt a recirculation procedure relying on the condenser-vacuum deaerator, or a separate deaerator, or a chemical scavenger, to remove or reduce the oxygen content of condenser water, prior to starting the steam generator and its feedwater supply. And when the steam-power cycle is in full operation, the condenser vacuum (ejector) pump will serve a scavenging function, removing some but not all of the dissolved gases.